To J. S. Henslow 2 September 1
Down. Farnborough | Kent.
My dear Henslow.
I have nothing to correct except that Bal. tintinnabulum cannot strictly be considered British, (being only an imported shell) except as a Crag Fossil.— I hardly know what to add as strictly British & living & breeding, perhaps Bal. porcatus would do as well as possible.— I may just mention, that in selecting these types I took the Pollicipes as giving all the characters of the whole order as well balanced as possible; but in the smaller groups I have picked out one eminently well characterized, or with every character by which the group is different from the other groups, most strongly pronounced.— I had thought the paper was only for the Ipswich Museum2 (though I cannot improve on it as it stands) & therefore I did not notice the two other Orders represented only by a single species each.3 I have inserted these in pencil, & you can determine whether to insert them in print; undoubtedly they ought to be, in order to give a full illustration of the Sub-class.—
Of the sub-class, including the three orders, it is impossible to give a type. I am sorry to have caused so much trouble, but I thought the paper was solely to guide you in your classification of the Ipswich Museum, & as you had not the two last orders, I purposely omitted all notice of them
Yours most truly | C. Darwin
Sends his comments on JSH’s MS on cirripedes ["On typical objects in natural history", Rep. BAAS (1855): 108–26].